X-ray fluoroscopy using an X-ray diagnostic apparatus is a technique of providing a user with a fluoroscopic image concerning an object, which is updated in real time. The user can observe the state of a moving organ, the manner of the flow of a contrast medium, and the like by visually recognizing the fluoroscopic image. In X-ray fluoroscopy, however, a portion around a region of interest of the object is irradiated with the same dose of X-rays as that for the region of interest, unnecessary exposure of the object to X-rays poses a problem. There is available spot fluoroscopy as a technique of suppressing such unnecessary exposure. Spot fluoroscopy is a technique of providing the user with the superimposed image obtained by superimposing a fluoroscopic image corresponding to a region of interest of an object, which is updated in real time, on a still image corresponding to a specific region of the object which is acquired by conventional X-ray fluoroscopy immediately before spot fluoroscopy. The user can observe the region of interest in real time while checking the position and the like of the region of interest in the specific region by visually recognizing the superimposed image. The irradiation range of X-rays under spot fluoroscopy is only a region of interest. It is therefore possible to suppress unnecessary exposure of an object as compared with conventional X-ray fluoroscopy. However, spot fluoroscopy does not allow real-time observation of a portion around a region of interest.
For this reason, there is a demand for real-time observation of also a portion around a region of interest while reducing the exposure dose of an object more than the related art. In order to meet this demand, it is a challenge to develop a technique of reducing the dose of X-rays on a portion around a region of interest relative to the dose of X-rays on the region of interest.